1. Field of the Invention
The present invention relates generally to the field of devices for collimating x-rays. More specifically, the present invention discloses a simplified shutter mechanism using a flexible band extending about a frame opening to directly control the position of two shutters.
2. Statement of the Problem
Shutter mechanisms for x-ray collimators present a unique set of design requirements. The shutters are typically made of a radio-opaque material, such as lead. This results in shutter plates that have substantial weight. In addition, x-ray diagnostic devices used in medical and dental offices are subject to .very tight space limitations. Therefore, the shutter mechanism must be as compact as possible. Finally, safety of the patient and health care providers is always a paramount concern. This dictates that the shutter mechanism must be capable of a high degree of positional accuracy to ensure an accurate x-ray dosage to the patient through a well-defined aperture and to prevent accidental exposure of others.
Existing shutter mechanisms have a number of shortcomings. Most commercially available shutter mechanisms for x-ray collimators involve a relatively complex linkage mechanism and/or a series of gears to move the shutter plates. This complexity increases the size, cost, and positional tolerances of the shutter mechanism, and can also lead to reliability problems.
A number of shutter mechanisms for x-ray collimators have been invented in the past, including the following:
______________________________________ Inventor U.S. Pat. No. Issue Date ______________________________________ Span et al. 5,012,506 Apr. 30, 1991 Hahn 4,641,335 Feb. 3, 1987 Holzermer 4,514,859 Apr. 30, 1985 Grass et al. 4,489,426 Dec. 18, 1984 Cutter 4,389,730 June 21, 1983 Cutter 4,380,820 Apr. 19, 1983 Hura 4,246,488 Jan. 20, 1981 Stodberg et al. 4,167,675 Sep. 11, 1979 Fekete 3,936,647 Feb. 3, 1976 Hura 3,829,701 Aug. 13, 1974 Peyser 3,609,370 Sep. 28, 1971 ______________________________________
Span et al. disclose a multileaf collimator having first and second pairs of leaves 30, 31 and 35, 36 at right angles. The leaves are independently adjustable.
Holzermer discloses an x-ray collimator with orthogonal rectangular diaphragm plates and a plurality of additional triangular diaphragm plates for pivotal movement into the four corner regions of the opening defined by the rectangular diaphragm plates. Each triangular plate is moved by a parallelogram linkage. The linkages are driven in unison by a stepper motor 47 and a continuous belt 45.
Hahn discloses a collimator for a stereo radiographic x-ray system with adjustable shutter leaves.
Grass et al. disclose another example of an x-ray collimator with an adjustable aperture.
The Cutter patents disclose two variations of a compact collimator with two orthogonally-disposed pairs of shutters. Mating inner edges of each pair move in a rectilinear path.
The Hura patents disclose two radiation collimators having orthogonal pairs of shutters that are driven by mechanical linkages.
Stodberg et al., Fekete, and Peyser disclose other examples of x-ray collimators using mechanical linkages and/or gears to control the position of shutters.
3. Solution to the Problem
None of the prior art references uncovered in the search show a simplified shutter mechanism for collimating x-rays that uses an elongated flexible band coupled to a drive means, such as a stepper motor, to directly control the position a pair of shutter plates without intermediate mechanical linkages or gears.